That changes in human vision occur throughout the lifespan now seems incontrovertible. The factors to which these changes can be attributed is, however, much less clear. The purpose of this research is to study some of the age changes in vision that occur in the elderly (60-80 years) under conditions that will allow us to separate prereceptoral, receptoral, and postreceptoral mechanisms. The prereceptoral factors that we will study with psychophysical methods include the absorption chaacteristics of the ocular media (primarily the lens and macular pigment) and the pupil. These factors selectively attenuate the light that can reach the receptors; any age-correlated changes in these prereceptoral factors would produce corresponding age-correlated changes in the retinal stimulus. Quantitative data on these age changes will allow us to present the same stimulus (specified at the receptors) for observers of all ages in order to then study age changes in receptoral and postreceptoral mechanisms. Receptoral mechanisms will be isolated by selective chromatic adaptation in order to measure (to a first approximation) the spectral sensitivity of each of the three classes of cone photoreceptor. We wish to know whether there are selective age changes in the sensitivity of the receptoral mechanisms. Our hypothesis is that the short-wave sensitive cones will show a selective reduction in sensitivity as a function of increasing age. At the postreceptoral level, we will isolate the luminance channel (which receives a combined input from the middle- and long-wave cones) and the chromatic channels (which receive input from all three cone types). These two postreceptoral mechanisms are associated with separate neural pathways. This research is thus concerned with separating neural and nonneural factors in the aging visual system. We believe that an understanding of these mechanisms will contribute not just to the study of vision, but to the general study of aging in sensory-neural systems.